The present invention relates to a device for programming an implantable electrode array used with an implantable stimulator. More particularly, one embodiment of the invention relates to a device used to provide directional programming for the implantable electrode array associated with an implantable stimulator that electrically stimulates the spinal cord for the purposes of controlling and reducing pain.
Within the past several years, rapid advances have been made in medical devices and apparatus for controlling chronic intractable pain. One such apparatus involves the implantation of an electrode array within the body to electrically stimulate the area of the spinal cord that conducts electrochemical signals to and from the pain site. The stimulation creates the sensation known as paresthesia, which can be characterized as an alternative sensation that replaces the pain signals sensed by the patient. One theory of the mechanism of action of electrical stimulation of the spinal cord for pain relief is the "gate control theory". This theory suggests that by simulating cells wherein the cell activity counters the conduction of the pain signal along the path to the brain, the pain signal can be blocked from passage.
Spinal cord stimulator and other implantable tissue stimulator systems come in two general types: "RF" controlled and fully implanted. The type commonly referred to as an "RF" system includes an external transmitter inductively coupled via an electromagnetic link to an implanted receiver that is connected to a lead with one or more electrodes for stimulating the tissue. The power source, e.g., a battery, for powering the implanted receiver-stimulator as well as the control circuitry to command the implant is maintained in the external unit, a hand-held sized device that is typically worn on the patient's belt or carried in a pocket. The data/power signals are transcutaneously coupled from a cable-connected transmission coil placed over the implanted receiver-stimulator device. The implanted receiver-stimulator device recess the signal and generates the stimulation. The external device usually has some patient control over selected stimulating parameters, and can be programmed from a physician programming system. An example of an RF system is described, e.g., in U.S. Pat. No. 4,793,353, incorporated herein by reference.
The fully implanted type of stimulating system contains the programmable stimulation information in memory, as well as a power supply, e.g., a battery, all within the implanted pulse generator, or "implant", so that once programmed and turned on, the implant can operate independently of external hardware. The implant is turned on and off and programmed to generate the desired stimulation pulses form an external programming device using transcutaneous electromagnetic, or RF links. Such stimulation parameters include, e.g., the pulse width, pulse amplitude, repetition rate, and burst rates. An example of such a commercially-available implantable device is the Medtronic Itrel II, Model 7424. Such device is substantially described in U.S. Pat. No. 4,520,825, also incorporated herein by reference.
The '825 patent describes a circuit implementation of a cyclic gradual turn on, or ramping of the output amplitude, of a programmable tissue stimulator. The implementation contains separate memory cells for programming the output amplitude and number of pulses at each increasing output level or "step". In devices of the type described in the referenced '825 patent, it is desirable to provide some means of control over the amplitude (intensity), the frequency, and the width of the stimulating pulses. Such control affords the patient using the device the ability to adjust the device for maximum effectiveness. For example, if the pulse amplitude is set too low, there may be insufficient pain relief for the user; yet, if the pulse amplitude is set too high, there may be an unpleasant or uncomfortable stinging or tingling sensation felt by the user. Moreover, the optimum stimulation parameters may change over time. That is, numerous and varied factors may influence the optimum stimulation parameters, such as the length of time the stimulation has been ON, user (patient) postural changes, user activity, medicines or drugs taken by the user, or the like.
In more complex stimulation systems, one or more leads can be attached to the pulse generator, with each lead usually having multiple electrode contacts, Each electrode contact can be programmed to assume a positive (anode), negative (cathode), or OFF polarity to create a particular stimulation field when current is applied. Thus, different combinations of programmed anode and cathode electrode contacts can be used to deliver a variety of current waveforms to stimulate the tissue surrounding the electrode contacts.
Within such complex systems, once one or more electrode arrays are implanted in the spinal cord, the ability to create paresthesia over the painful site is firstly dependent upon the ability to accurately locate the stimulation site. This may more readily be accomplished by programming the selection of electrode contacts within the array(s) than by physically maneuvering the lead (and hence physically relocating the electrode contacts). Thus, the electrode arrays may be implanted in the vicinity of the target site, and then the individual electrode contacts within the array(s) are selected to identify an electrode contact combination that best addresses the painful site. In other words, electrode programming may be used to pinpoint the stimulation area correlating to the pain. Such electrode programming ability is particularly advantageous after implant should the lead contacts gradually or unexpectedly move, thereby relocating the paresthesia away from the pain site. With electrode programmability, the stimulation area can often be moved back to the effective site without having to re-operate on the patient in order to reposition the lead and its electrode array.
Electrode programming has provided different clinical results using different combinations of electrode contacts and stimulation parameters, such as pulse width, amplitude and frequency. Hence, an effective spinal cord stimulation system should provide flexible programming to allow customization of the stimulation profile for the patient, and thereby allow for easy changes to such stimulation profile over time, as needed.
The physician generally programs the implant, external controller, and/or external patient programmer through a computerized programming station. This programming system can be a self-contained hardware/software system, or can be defined predominately by software running on a standard personal computer (PC). The PC or custom hardware can have a transmitting coil attachment to allow for the programming of implants, or other attachments to program external units. Patients are generally provided hand-held programmers that are more limited in scope than are the physician-programming systems, with such hand-held programmers still providing the patient with some control over selected parameters.
Programming of the pulse generators, or implants, can be divided into two main programming categories: (1) programming of stimulation pulse variables, and (2) programming electrode configurations. Programmable stimulation pulse variables, as previously indicated, typically include pulse amplitude, pulse duration, pulse repetition rate, burst rate, and the like. Programmable electrode configuration includes the selection of electrodes for simulation from the available electrode contacts within the array as well as electrode polarity (.+-.) assignments. Factors to consider when programming an electrode configuration include the number of electrode contacts to be selected, the polarity assigned to each selected electrode contact, and the location of each selected electrode contact within the array relative to the spinal cord, and the distance between selected electrodes (anodes and cathodes), all of which factors combine to define a stimulation field. The clinician's electrode selection results in a simulating "group": containing at least one anode and at least one cathode that can be used to pass stimulating currents defined by the programmed pulse variables. For an electrode array having eight electrode contacts, this can result in an unreasonable large number of possible combinations, or stimulation groups, to chose from.
Moreover, within each stimulation group, there are a large number of pulse stimulation parameters that may be selected. Thus, through the programmer, the clinician must select each electrode, including polarity, for stimulation to create each combination of electrode contacts for patient testing. Then, for each combination, the clinician adjusts the stimulation parameters for patient feedback until the optimal pain relief is found for the patient. Disadvantageously, it is difficult to test many stimulation variables with hundreds or even thousands of possible electrode and stimulus parameter combinations. To test all such combinations, which is typically necessary in order to find the optimum stimulation settings, is a very lengthy and tedious process. However, because it is lengthy and tedious, some clinicians may not bother to test many different electrode combinations, including many that may be considered far more optimal than what is ultimately programmed for the patient. It is thus evident that there is a need in the art for a more manageable programming technique for testing and handling a large number of possible electrode and pulse parameter combinations.
One method that has recently been developed for simplifying the programming process is described in U.S. Pat. No. 5,370,672, incorporated herein by reference. The '672 patent describes a programming system where the patient interacts with the clinician's programmer. More specifically, the '672 patent teaches a system wherein the patient identifies the pain site by drawing on a touch screen displaying an illustration of the human body. After entering the patient's stimulation thresholds and associated tolerances into the system, the computer generates a recommended electrode configuration for that patient using algorithms based on spinal cord stimulation research. The patient responds to the resulting stimulation by drawing the amount of paresthesia coverage over the body illustration. If the drawing paresthesia site does not fully match the pain site, the system adjusts the recommendation and the patient responds again to the new sense of paresthesia. This process is repeated until the best-tested settings are reached.
Advantageously, the process described in the '672 patent electively eliminates the manual selection of electrode combinations, and reduces the selection process to a reasonable testing of electrode/parameter combinations based on an extensive pre-organized set of rules for programming optimization and patient input. Moreover, the physician/clinician is not directly controlling the programming session; rather, the patient provides the system with the feedback without the need for the physician or clinician to interpret the patient's sensations or empirically estimate changes required in stimulation parameters.
Disadvantageously, using the method described in the '672 patent, the patient must still test and respond to each of the chosen combinations and must depend upon the system recommendations, which system recommendations might exclude an possible optimal setting for that patient. Further, the patient must be able to accurately translate subtle sensations and differences to a drawing on a screen, and then wait for device programming before having to react and redraw the paresthesia from the new settings. Such process can still be time consuming. Furthermore, subtle sensation differences felt by the patient between combinations cannot necessarily be translated in a drawing of paresthesia that only address "coverage area." In summary, by reducing the combinations to a computer-generated recommendation, many electrode combinations might be omitted that could provide a more effective paresthesia. Hence, the process of computer-recommended combinations, although superior to manual arbitrary selection, can still be viewed as an undesirable "discrete" method of patient feedback evaluation: i.e., electrodes are programmed and patient feedback is entered for each combination, one iteration at a time.
In view of the above, it is evident that profound improvements are still needed in the way multiple implanted electrode combinations are programmed. In particular, it is seen that improvements in programming techniques and methods are needed that do not compromise the patient's ability to feel the subtle effects of many different combinations, and that provide a more immediately responsive programming-to-feedback loop.